Abstract

Authentication is the primary function used to reduce the risk of illegitimate access to IT services of any organisation. Kerberos is a widely used authentication protocol for authentication and access control mechanisms.

This thesis presents the development of security strategies using Kerberos authentication protocol in wireless networks, Kerberos-Key Exchange protocol, Kerberos with timed-delay, Kerberos with timed-delay and delayed decryption, Kerberos with timed-delay, delayed decryption and password encryption properties. This thesis also includes a number of other research works such as, frequently key renewal under pseudo-secure conditions and shut down of the authentication server to external access temporarily to allow for secure key exchange.

A general approach for the analysis and verification of authentication properties as well as Kerberos authentication protocol are presented. Existing authentication mechanisms coupled with strong encryption techniques are considered, investigated and analysed in detail. IEEE 802.1x standard, IEEE 802.11 wireless communication networks are also considered. First, existing security and authentication approaches for Kerberos authentication protocol are critically analysed with the discussions on merits and weaknesses. Then relevant terminology is defined and explained.

Since Kerberos exhibits some vulnerabilities, the existing solutions have not treated the possibilities of more than one authentication server in a strict sense. A three way authentication mechanism addresses possible solution to this problem. An authentication protocol has been developed to improve the three way authentication mechanism for Kerberos. Dynamically renewing keys under pseudo-secure situations involves a temporary interruption to link/server access. After describing and analysing a protocol to achieve improved security for authentication, an analytical method is used to evaluate the cost in terms of the degradation of system performability. Various results are presented.An approach that involves a new authentication protocol is proposed. This new approach combines delaying decryption with timed authentication by using passwords and session keys for authentication purposes, and frequent key renewal under secure conditions. The analysis and verification of authentication properties and results of the designed protocol are presented and discussed.Protocols often fail when they are analysed critically. Formal approaches have emerged to analyse protocol failures. Abstract languages are designed especially for the description of communication patterns. A notion of rank functions is introduced for analysing purposes as well. An application of this formal approach to a newly designed authentication protocol that combines delaying the decryption process with timed authentication is presented.Formal methods for verifying cryptographic protocols are created to assist in ensuring that authentication protocols meet their specifications. Model checking techniques such as Communicating Sequential Processes (CSP) and Failure Divergence Refinement (FDR) checker, are widely acknowledged for effectively and efficiently revealing flaws in protocols faster than most other contemporaries. Essentially, model checking involves a detailed search of all the states reachable by the components of a protocol model. In the models that describe authentication protocols, the components, regarded as processes, are the principals including intruder (attacker) and parameters for authentication such as keys, nonces, tickets, and certificates. In this research, an automated generation tool, CASPER is used to produce CSP descriptions. Proposed protocol models rely on trusted third parties in authentication transactions while intruder capabilities are based on possible inductions and deductions. This research attempts to combine the two methods in model checking in order to realise an abstract description of intruder with enhanced capabilities. A target protocol of interest is that of Kerberos authentication protocol.The process of increasing the strength of security mechanisms usually impacts on performance thresholds. In recognition of this fact, the research adopts an analytical method known as spectral expansion to ascertain the level of impact, and which resulting protocol amendments will have on performance. Spectral expansion is based on state exploration. This implies that it is subject, as model checking, to the state explosion problem. The performance characteristics of amended protocols are examined relative to the existing protocols.